1. Field of the Invention
The present invention relates to a position measuring laser apparatus for measuring the position of an unmanned moving vehicle to control its course.
2. Description of the Related Art
An unmanned moving vehicle repeatedly moved between locations is used in work area such as a mine. For example, an operator first operates a vehicle to move in a predetermined course. The vehicle""s position is measured by a GPS (global positioning system). The measured position is stored as a target position in memory. Thereafter, the moving vehicle is allowed to move without any assistance of the operator. The GPS measures and compares the position of the moving vehicle with the target position stored in memory. Consequently, a vehicle-mounted computer controls the operation of the unmanned moving vehicle based on the difference between the measured position and the target position. This enables the unmanned moving vehicle to automatically move toward the target position.
However, the GPS introduces errors within a certain range, and therefore, it is difficult to control the movement of the unmanned moving vehicle accurately. To eliminate the GPS errors and correct the position of the unmanned moving vehicle, a position measuring laser apparatus for measuring the position of the unmanned moving vehicle is introduced. The apparatus is coupled with the GPS system to achieve highly accurate movement of the unmanned vehicle.
FIGS. 8(a) and 8(b) illustrate the measurement and correction of the position of an unmanned moving vehicle using the position measuring laser apparatus. For example, an unmanned truck AC has a position measuring laser apparatus 1 mounted. The apparatus can emit laser beams at a required angle in two directions and can detect each of laser beams incident in the two directions. Furthermore, retroreflectors RR are provided at specific intervals for reflecting the incident laser beam at an angle of 180xc2x0 in a direction along a moving course of the unmanned truck AC. As indicated by a solid line of FIG. 8(b), the position measuring laser apparatus 1 emits a laser beam forward at the required angle and then detects the laser beam reflected from the retroreflector RR. Moreover, as indicated by a chained line of FIG. 8(b), when the unmanned truck AC moves by a predetermined distance, the position measuring laser apparatus 1 emits a laser beam sideways and then detects the laser beam reflected from the retroreflector RR. Consequently, the position of the unmanned truck AC with respect to the retroreflector RR can be calculated by a trigonometric relation using a movement distance L of the unmanned truck AC and the angle defined by the two laser beams. In this manner, as shown in FIG. 8(a), the direction of the unmanned truck AC is controlled while the position is detected so that the detected position coincides with the predetermined position, thus achieving highly accurate movement.
A visible light beam can be used as the laser beam. However, this may pose a problem in that the position may not be accurately detected when the position measuring laser apparatus receives a light beam other than the intended reflected laser beam. As a result, it becomes necessary to limit the detection of laser beam to that emitted from the position measuring laser apparatus for the purpose of positional detection.
Often, the moving system for the unmanned vehicle of this type is often used under extreme conditions. In particular, the position measuring laser apparatus is required to securely emit the laser beam even in hot or cold regions. Moreover, the angles of the laser beams emitted should be controlled to a high degree because a small deviation can introduce a significant error in the measured position. Additionally, the window of the apparatus through which beams are emitted or received needs to be cleaned every time it becomes dirty under the extreme conditions.
The present invention relates to a position measuring laser apparatus capable of measuring the position of an unmanned vehicle with high accuracy by eliminating any influence of an outside light beam. Furthermore, the present invention relates to a position measuring laser apparatus capable of securely measuring a position irrespective of temperatures of outside environment. Moreover, the present invention relates to a position measuring laser apparatus that can be easily set on an unmanned moving vehicle and maintained.
According to the present invention, a position measuring laser apparatus is provided with a first and a second laser transmitter-receiver, each having its optical axis oriented at a required angle toward a moving body such as an unmanned moving vehicle, each of the laser transmitter-receivers including laser beam emitting means for emitting a laser beam and laser beam receiving means for receiving a laser beam resulting from the emitted laser beam reflected on a reference reflecting mirror, in which the position of the moving body with respect to the reference reflecting mirror is measured based on a beam receiving signal indicative of each of the laser beams obtained by both of the laser transmitter-receivers. The apparatus further includes position measuring means for comparing a drive signal for driving the laser beam emitting means with a beam receiving signal generated by the laser beam receiving means for measuring the position of the moving body based on the beam receiving signal when both of the signals coincide. In particular, the position measuring means includes: means for outputting the drive signal having a required frequency to the laser beam emitting means; timing generating means for generating a timing signal to be set based on the frequency of the drive signal; coincidence detecting means for comparing the beam receiving signal with the drive signal based on the timing signal to detect the coincidence therebetween; and outputting means for outputting the beam receiving signal as an effective beam receiving signal when the coincidence is detected in sequentially predetermined times by the coincidence detecting means.
Furthermore, the position measuring laser apparatus can be implemented according to the following embodiments: first, the laser beam emitting means is constituted in the form of a laser module incorporating a laser diode therein, wherein the laser module is detachably attached to a Peltier element fixingly housed inside the laser transmitter-receiver and the optical axis of the laser module is positionally adjusted; second, the laser transmitter-receivers are fixingly supported by one fixing plate, wherein each of the laser transmitter-receivers is fixingly supported by the fixing plate by mutual engagement between projections formed at either one of the laser transmitter-receiver and the fixing plate and recessed grooves formed at the other thereof, in which the projection and the recessed groove are provided for determining an optical axis direction of each of the laser transmitter-receivers; and third, the laser transmitter-receiver is provided with a window opened for transmitting the laser beam, and a transparent plate detachably attached to the laser transmitter-receiver in front of the window.
In the position measuring laser apparatus, the drive signal output at the time of laser emission is compared with the beam receiving signal generated when the laser beam is detected. If the signals coincide with each other, that is, if the signals coincide with each other in sequentially predetermined times, the beam receiving signal is determined as from a laser beam that was emitted from the laser beam emitting means and reflected on the reference reflecting mirror. Thus, the position of the moving body can be measured with high accuracy without being influenced by other light beams. Moreover, if the first to third embodiments are used, the position can be securely measured irrespective of the outside temperatures. Also, the position measuring laser apparatus can be easily set with respect to the unmanned moving vehicle for easy maintenance.